When an impression of an oral cavity is taken for manufacturing a prosthesis in dental treatment, impression materials such as silicone impression materials and alginate impression materials are generally used. In that case, an impression tray is used for inserting and holding an impression material in the oral cavity. That is, an impression material is placed on the impression tray and inserted in the oral cavity of a patient. The impression material is pressed to the oral cavity, whereby the shape of the oral cavity is transferred to the impression material. After the impression material is set, the impression tray is taken out from the oral cavity, integrally with the impression material on which the shape of the oral cavity is transferred, the impression material being held by the impression tray.
In a case where an impression of an edentulous patient (including a patient nearly edentulous) is to be taken, it is needed to take an impression of the alveolar ridge having smooth curved surfaces. In that case, a very high accuracy is required, for example, an impression material needs to be pressed with a uniform strength. Therefore, in many cases, the taking impression for an edentulous patient is carried out twice, in order to take the impression of the oral cavity with a better accuracy.
Especially, the first impression taking of the alveolar ridge is carried out with a general impression tray. Thereafter, a model of the edentulous jaw is made based on the set impression.
Then, from the model of the edentulous jaw, a “personal tray” which is an impression tray only for the edentulous patient is made. Then, an impression material is thinly placed on the personal tray, and the second impression taking of the alveolar ridge is carried out. From the impression, an accurate model of the edentulous jaw is made.
In conventional ways, a plaster model is obtained from a plaster poured into the personal tray. However, with the development of digitization technology and CAD technology, a technique of obtaining three-dimensional shape data of the obtained impression and processing the data on computer has come out recently, as described in Patent Literature 1 for example. With this technique, it is possible to adjust the shape of a dental prosthesis to a final shape on computer, and to send the data of the final shape to an NC machine, to thereby directly produce a final product.
In addition, in order to properly arrange the main body of the impression tray in the oral cavity of a patient, a handle is provided on the impression tray at a portion to be a labial side, extending in such a way as to project outside the oral cavity, as shown in Patent Literature 2.